You can use the IETF Class value (att 25) to pass along a string to the asa, using this string, you can have the ASA to place the user on a specific group-policy that matches that string and in the group-policy you can have the tunnel-protocol svc or webvpn enabled or not. When the user that should not be connecting via anyconect receives the string and the asa places the user on the group-policy that does not have that tunnel protocol enabled, the connection will never happen.